High-voltage polymer electrolyte membrane as well as preparation method and application thereof

Abstract

The invention discloses a high-voltage polymer electrolyte membrane as well as a preparation method and application thereof. The polymer electrolyte membrane comprises a nanofiber membrane substrate and a solid electrolyte membrane, wherein the nanofiber membrane substrate is formed by polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and the solid electrolyte membrane is formed on the substrate. According to the preparation method, double bond free radical polymerization (DBRP) and ring opening polymerization (ROP) are combined, polymerization is carried out on a polymer framework prepared through electrostatic spinning of PVDF-HFP and PVDF (PHP), and therefore the polymer electrolyte is prepared, and the polymer electrolyte achieves advantage complementation in the aspects of side chain functionality, network structure stability and high voltage resistance. The polymer electrolyte membrane still has good oxidation stability in a voltage environment of 4.5 V or above. According to the electrolyte membrane, pre-polymerization and secondary polymerization are performed on an electrospinning framework to form a topological entangled cross-linked network structure, so that the electrolyte membrane shows excellent mechanical strength and electrochemical stability in a high-voltage lithium metal battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid-state batteries, and in particular relates to a high-voltage polymer electrolyte membrane and a preparation method and application thereof. Background Art

[0002] With the rapid development of portable electronic devices, electric vehicles, and large-scale energy storage systems, the demand for high-energy-density lithium-ion batteries has increased significantly. Although traditional liquid electrolytes have high ionic conductivity, they have obvious safety risks, such as leakage, flammability, and volatility, which seriously restrict their widespread application in high-energy-density and high-voltage systems. To overcome the above-mentioned defects, solid polymer electrolytes have gradually become a research hotspot. Due to their inherent non-flammability, excellent mechanical properties, good flexibility, and electrochemical stability, solid polymer electrolytes are considered to be an ideal choice to replace liquid electrolytes and achieve high-safety and high-energy-density batteries. However, the current mainstream polymer solid electrolytes, such as polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), are prone to electrochemical decomposition under high-voltage conditions (e.g., above 4.5V), showing the defect of insufficient electrochemical stability, which seriously limits their practical application in high-voltage batteries.

[0003] Therefore, the development of high-voltage polymer solid electrolytes that can maintain excellent electrochemical stability under high voltage environments, effectively inhibit the decomposition of the polymer matrix and have high ionic conductivity has become an important technical issue to promote the practical application of the next generation of high-energy-density solid-state lithium metal batteries. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a polymer electrolyte membrane that can circulate stably under high-voltage environment, a preparation method thereof, and a solid-state lithium-ion battery using the polymer electrolyte membrane. The preparation method combines double bond radical polymerization (DBRP) and ring-opening polymerization (ROP), and polymerizes on a polymer framework prepared by electrospinning PVDF-HFP@PVDF (PHP) to prepare the polymer electrolyte. The polymer electrolyte achieves complementary advantages in side chain functionality, network structure stability and high-voltage resistance.

[0005] According to one aspect of the present invention, an object of the present invention is to provide a polymer electrolyte membrane, the polymer electrolyte membrane comprising a nanofiber membrane substrate formed of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and a solid electrolyte membrane formed on the substrate, wherein the solid electrolyte membrane is formed by secondary polymerization of vinyl ethylene carbonate (VEC), 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the degree of polymerization of the solid electrolyte membrane is 65 to 70%, and the thickness of the nanofiber membrane substrate is 3-8 μm. The ratio of the polymer mass of the solid electrolyte membrane to the area of ​​the nanofiber membrane substrate is 6-7 g:90-110 cm -2 .

[0006] Preferably, the ionic conductivity of the solid electrolyte membrane at room temperature is greater than 0.5 mS / cm.

[0007] According to the second aspect of the present invention, another object of the present invention is to provide a method for preparing the polymer electrolyte membrane, comprising the following steps:

[0008] S1. Preparation of electrospun skeleton nanofiber membrane: Dissolve polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone to prepare an electrospinning solution with a total concentration of 5-10 wt%; Stir at 40-60°C for 24-72 hours, filter and degas, spin through an electrospinning apparatus to obtain a nanofiber membrane with a thickness of 3-8 μm, and dry at 70-90°C;

[0009] S2. Preparation of the polymer bulk: vinyl ethylene carbonate (VEC), 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were mixed in a molar ratio of 1:(0.5-2):(0.1-0.5), and azobisisobutyronitrile (AIBN) was added as an initiator, the amount of azobisisobutyronitrile was 0.5-1.5% of the total weight of the monomers, after deoxygenation by Schlenk tube treatment, prepolymerized at 60-70 ° C for 4-8 hours, and then stannous octoate (Sn(Oct) 2 was added as a crosslinking catalyst, the amount of stannous octoate was 0.5-2% of the total weight of the prepolymer, and the temperature was raised to 75-85 ° C for coordination polymerization for 10-14 hours to obtain a fluorinated copolymer solution;

[0010] S3. Membrane formation: Cast the polymer solution obtained in step S2 onto the nanofiber membrane in step S1, and heat and cure it at 70-90°C under vacuum for 12-24 hours to form a composite solid polymer electrolyte membrane. The ratio of the polymer mass of the solid electrolyte membrane to the base area of ​​the nanofiber membrane is 6-7g:90-110cm -2 .

[0011] Preferably, in step S1, the mass ratio of polyvinylidene fluoride (PVDF) to polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is (8-9.5):(0.5-2);

[0012] Preferably, in step S1, the volume ratio of N,N-dimethylformamide to acetone is (6-8):(2-4);

[0013] Preferably, in step S1, the spinning conditions are as follows: voltage 8-12 kV, distance between the needle and the receiving device 10-15 cm, and ambient humidity ≤10%.

[0014] Preferably, the deoxygenation treatment in step S2 is specifically as follows: freezing with liquid nitrogen, evacuating to a pressure of ≤10 Pa, and introducing nitrogen to restore to normal pressure, and repeating the operation at least 3 times.

[0015] Preferably, the thickness of the film formed during casting in step S3 can be adjusted by controlling the viscosity of the casting solution and the porosity of the electrospun skeleton nanofiber membrane, and the thickness of the obtained electrolyte membrane is in the range of 5-50 μm.

[0016] According to the third aspect of the present invention, another object of the present invention is to provide a use of the polymer electrolyte membrane as an electrolyte in a solid-state lithium battery.

[0017] According to the fourth aspect of the present invention, another object of the present invention is to provide a solid-state lithium battery, wherein the solid-state lithium battery adopts the polymer electrolyte membrane according to the present invention as an electrolyte.

[0018] Preferably, the positive electrode sheet in the solid-state lithium battery is a lithium-rich manganese-based or high-nickel ternary positive electrode material, and the negative electrode sheet is one of a lithium sheet, a lithium alloy or hard carbon.

[0019] More preferably, the positive electrode sheet is made of one of lithium cobalt oxide, lithium iron phosphate, and nickel cobalt manganese.

[0020] Beneficial effects

[0021] The polymer electrolyte membrane according to the present invention contains fluorinated side chains and polar functional groups, and exhibits excellent oxidative stability at voltages above 4.5 V. The electrolyte membrane forms a topologically entangled cross-linked network structure through pre-polymerization and secondary polymerization on an electrospun skeleton, resulting in excellent mechanical strength and electrochemical stability in high-voltage lithium metal batteries.

[0022] The preparation method according to the present invention combines a segmented polymerization strategy with an electrospun skeleton to prepare a polymer electrolyte that achieves complementary advantages in terms of side chain functionality (ion transport, protonation anchoring, etc.), network structure stability (topological entanglement enhances toughness and maintains a continuous transmission path), and high-voltage resistance (fluorinated or highly antioxidant side chains and a wide electrochemical window). This enables it to exhibit potential outstanding performance in lithium metal battery applications with high energy density, long cycle life, and high safety, providing strong support for the research and industrialization of next-generation high-voltage solid-state lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 1 are SEM images of the C-PE film prepared in Example 1 under a scanning electron microscope (surface morphology and cross-sectional morphology, respectively).

[0025] Figure 2 Impedance spectra of the electrolyte membranes of Examples 1 to 3 at room temperature.

[0026] Figure 3 Liquid NMR of C-PE (Example 1) prepared by the present invention 1 Table of H NMR and degree of polymerization (DOA) results for PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3), and C-PE.

[0027] Figures 4a to 4d The VEC, PVEC (Comparative Example 1), C-PVEC (Comparative Example 2) and P (VEC-TFPMA) (Comparative Example 3) prepared by the present invention are 1 H NMR spectrum.

[0028] Figure 5FTIR infrared spectra of the PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared in the present invention.

[0029] Figure 6 Differential scanning calorimetry (DSC) measurements of the PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared according to the present invention.

[0030] Figure 7 Gel permeation chromatography (GPC) of the PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared in the present invention, as well as the weight average molecular weight (Mw) and number average molecular weight (Mn) of each polymer obtained by the test analysis.

[0031] Figure 8 Thermogravimetric analysis (TG or TGA) of the PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared in the present invention.

[0032] Figure 9 The ionic conductivity of the electrolyte membranes prepared by the present invention is PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), and P(VEC-TFPMA) (Comparative Example 3). Figure 2 Compared with the C-PE (Example 1) in the embodiment, it is confirmed that the embodiment after secondary polymerization has the best room temperature ionic conductivity.

[0033] Figure 10 The lithium symmetric battery assembled with the PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared by the present invention was tested at 0.1 mA cm -2 Long cycle test at different current densities.

[0034] Figure 11 The left figure shows the PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared by the present invention assembled with LRMO positive electrode materials with a cut-off voltage of 4.8V to test their cycle performance at a rate of 0.2C. The right figure shows the P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes prepared by the present invention assembled with LRMO positive electrode materials with a cut-off voltage of 4.8V to test their rate performance. DETAILED DESCRIPTION

[0035] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims are not to be construed as limited to their general and dictionary meanings, but rather should be interpreted based on the meanings and concepts corresponding to the technical aspects of the present invention, based on the principle that allows the inventor to appropriately define the terms for the best interpretation. Therefore, the description herein is merely a preferred example for illustrative purposes and is not intended to limit the scope of the present invention. It should be understood that other equivalent implementations and modifications may be made without departing from the spirit and scope of the present invention.

[0036] As used herein, the terms "comprises," "includes," "has," "contains" or any other similar terms are open conjunctions that are intended to cover non-exclusive inclusions. For example, a composition or article containing multiple elements is not limited to the elements listed herein, but may also include other elements that are not explicitly listed but are generally inherent to the composition or article. In addition, unless expressly stated to the contrary, the term "or" refers to an inclusive "or" rather than an exclusive "or." For example, any of the following situations satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist). In addition, as used herein, the terms "comprises," "includes," "has," and "contains" should be interpreted as specifically disclosed and simultaneously cover closed or semi-closed conjunctions such as "consisting of" and "consisting essentially of."

[0037] Throughout this document, all features or conditions defined as numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered to encompass and specifically disclose all possible subranges and individual values ​​within those ranges, particularly integer values. For example, a description of a range "1 to 8" should be considered to specifically disclose all possible subranges such as 1 to 7, 2 to 8, 2 to 6, 3 to 6, 4 to 8, 3 to 8, and so forth, particularly those defined by all integer values, and should be considered to specifically disclose individual values ​​within those ranges such as 1, 2, 3, 4, 5, 6, 7, and 8. Unless otherwise indicated, the foregoing interpretation applies to all of the present disclosure, regardless of whether the ranges are comprehensive or not.

[0038] If a quantity or other value or parameter is expressed as a range, a preferred range, or a series of upper and lower limits, it should be understood that all ranges consisting of any upper limit or preferred value of the range and any lower limit or preferred value of the range have been specifically disclosed herein, regardless of whether these ranges are disclosed separately. In addition, when a numerical range is mentioned herein, unless otherwise specified, the range should include its endpoints and all integers and fractions within the range.

[0039] In this document, numerical values ​​should be understood to have the accuracy of the number of significant digits of the numerical value, provided that the purpose of the invention can be achieved. For example, the number 40.0 should be understood to cover the range from 39.50 to 40.49.

[0040] In addition, unless otherwise specified, the reagents and solvents disclosed below were purchased from Sigma-Aldrich Korea, FT-IR was measured by using FT-IR 4100 series from Jasco; HPLC was measured by using 1200 series from Agilent Technologies; and 1 H NMR was measured using an Oxford NMR 300 MHz spectrometer from Varian Mercury Instruments. Purity was calculated as area % by HPLC; Tg was measured using a Netzsch DSC 200F3; GPC was measured using an Agilent PL-GPC50; and TGA was measured using a TG 290F3.

[0041] The following examples are merely examples of embodiments of the present invention and do not constitute any limitation thereto. Those skilled in the art will appreciate that modifications without departing from the spirit and scope of the present invention fall within the scope of protection of the present invention. Unless otherwise specified, the reagents and instruments used in the following examples are commercially available products.

[0042] Raw materials and reagents: All raw materials used were of analytical grade, including vinyl carbonate (VEC), stannous octoate (Sn(Oct)2), acetone, polyvinylidene fluoride (PVDF), and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP). In addition, 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA), ethanol, azobisisobutyronitrile (AIBN), and N,N-dimethylformamide (DMF) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and lithium bistrifluoromethanesulfonyl imide (LiTFSI) and lithium-rich manganese-based oxide (LRMO) were purchased from Suzhou Duoduo Chemical Technology Co., Ltd.

[0043] S1. Preparation of Electrospun Skeleton Nanofiber Membranes

[0044] 7.2 g of PVDF and 0.8 g of PVDF-HFP were dissolved in a mixed solvent of 64.4 g of DMF and 27.6 g of acetone (mass ratio: PVDF:PVDF-HFP = 9:1, DMF:acetone = 7:3). The mixture had a total concentration of 8 wt% of PVDF and PVDF-HFP. After stirring at 50°C for 48 hours, the mixture was filtered and allowed to stand for degassing. Electrospinning was performed using a syringe pump flow rate of 1 mL / h, a needle-to-receiving roller distance of 13 cm, a voltage of 10 kV, a roller speed of 5 rpm, an ambient temperature of 20°C, and a humidity of 5%. The membrane was spun for 0.5 hours to obtain a nanofiber membrane with a thickness of approximately 5 ± 2 μm, which was then dried at 80°C.

[0045] Example 1:

[0046] Step (1): Prepolymerization: Weigh 4.00 g of VEC and 0.37 g of TFPMA, and add 1.748 g of LiTFSI. Add 0.0437 g of AIBN as an initiator and place in a Schlenk reaction tube. Quickly freeze the mixture with liquid nitrogen, evacuate the mixture using a double-row tube, and repeatedly introduce nitrogen three times. Place the reaction tube in an oil bath and stir at 65°C for 6 h to complete the prepolymerization and obtain the P(VEC-TFPMA) prepolymer.

[0047] Step (2): Secondary Polymerization: Add 0.04 g of Sn(Oct)2 to the P(VEC-TFPMA) prepolymer obtained in step (1), and again evacuate and purge with nitrogen three times. Stir at 65°C for 3 h to thoroughly and evenly mix the catalyst and prepolymer to obtain a fluorinated copolymer C-PE solution.

[0048] Step (3): Membrane preparation: The fluorinated copolymer C-PE solution obtained in step (2) was uniformly poured onto the surface of the pre-prepared PVDF-HFP-PVDF electrospun nanofiber membrane. The ratio of the solution to the nanofiber membrane substrate area was 6.3817 g:100 cm -2 The solid polymer electrolyte membrane (C-PE membrane) was obtained by heating it in a high vacuum oven at 80°C for 24 hours. The ionic conductivity at room temperature was 0.81 mS cm -1 .

[0049] Example 2:

[0050] Step (1): Prepolymerization: 4.00 g of VEC and 0.55 g of TFPMA were weighed, and 1.748 g of LiTFSI was added. After adding 0.0437 g of AIBN, the mixture was frozen in liquid nitrogen, vacuumed, and purged with nitrogen in the same manner as in Example 1. The prepolymerization was completed by stirring at 65°C for 6 h to obtain a P(VEC-TFPMA) prepolymer.

[0051] Step (2): Secondary Polymerization: After prepolymerization, 0.04 g of Sn(Oct)2 was added to the P(VEC-TFPMA) prepolymer obtained in step (1), and the mixture was again vacuumed and purged with nitrogen three times. The mixture was stirred at 65°C for 3 h to allow the catalyst and prepolymer to be thoroughly and evenly mixed, thereby obtaining a fluorinated copolymer C-PE solution.

[0052] Step (3): Membrane preparation: The fluorinated copolymer C-PE solution obtained in step (2) was evenly poured onto the surface of the pre-prepared PVDF-HFP-PVDF electrospun nanofiber membrane. The ratio of the solution to the nanofiber membrane substrate area was 5 ml:100 cm -2 Place in a high vacuum oven and heat at 80°C for 24 hours to complete secondary polymerization and curing. A solid polymer electrolyte membrane (C-PE membrane) is obtained. The ionic conductivity at room temperature is 0.35 mS cm -1 .

[0053] Example 3

[0054] Step (1): Prepolymerization: Weigh 4.00 g of VEC and 0.20 g of TFPMA, and add 1.748 g of LiTFSI. Add 0.0437 g of AIBN, and perform the same freezing, vacuuming, and nitrogen purge procedures in a Schlenk tube. Stir at 65°C for 6 h to complete the prepolymerization, yielding the P(VEC-TFPMA) prepolymer.

[0055] Step (2): Secondary Polymerization: After prepolymerization, 0.04 g of Sn(Oct)2 was added to the P(VEC-TFPMA) prepolymer obtained in step (1), and the mixture was again vacuumed and purged with nitrogen three times. The mixture was stirred at 65°C for 3 h to allow the catalyst and prepolymer to be thoroughly and evenly mixed, thereby obtaining a fluorinated copolymer C-PE solution.

[0056] Step (3): The fluorinated copolymer C-PE solution obtained in step (2) is uniformly poured onto the surface of the pre-prepared PVDF-HFP-PVDF electrospun nanofiber membrane. The ratio of the solution to the nanofiber membrane substrate area is 5 ml:100 cm-2. Place in a high vacuum oven and heat at 80°C for 24 hours to complete secondary polymerization and curing. A solid polymer electrolyte membrane (C-PE) is obtained. The ionic conductivity at room temperature is 0.29 mS cm -1 .

[0057] Comparative Example 1 (PVEC membrane):

[0058] Step (1) was prepolymerized in the same manner as in step (1) of Example 1, except that TFPMA was not added and only VEC and LiTFSI were used;

[0059] Step (2) The secondary polymerization step of step (2) in Example 1 is omitted;

[0060] Step (3) After the prepolymer solution obtained in step (1) is poured into the electrospun membrane, it is heated in vacuum at 80°C for 12 hours in the same manner as step (3) in Example 1 to form a membrane (only for PVEC membrane). The ionic conductivity at room temperature is 0.11 mS cm -1 .

[0061] Comparative Example 2 (C-PVEC membrane):

[0062] Step (1) The prepolymerization was carried out in the same manner as in step (1) of Example 1, except that TFPMA was not added and AIBN was replaced by Sn(Oct)2;

[0063] Step (2) The secondary polymerization step of step (2) in Example 1 is omitted;

[0064] Step (3) is to form a film (only C-PVEC film) according to the same film forming process as step (3) of comparative example 1. The ionic conductivity at room temperature is 0.17 mS cm -1 .

[0065] Comparative Example 3 (P(VEC-TFPMA) membrane):

[0066] Step (1): prepolymerization was carried out in the same manner as step (1) of Example 1;

[0067] Step (2) is omitted. The secondary polymerization step is omitted in step (2) of Example 1;

[0068] Step (3) is to form a film (only P(VEC-TFPMA) film) in the same film forming process as step (3) of comparative example 1. The ionic conductivity at room temperature is 0.22 mS cm -1 .

[0069] Test application examples

[0070] The composite solid electrolyte membranes prepared in Example 1 and Comparative Examples 1 to 3 were cut into discs with a diameter of 19 mm and assembled into button cells. The positive electrode of the assembled battery was a lithium-rich manganese-based oxide positive electrode (LRMO) with a diameter of 12 mm, and the negative electrode was a metal lithium sheet with a diameter of 12 mm. Electrochemical performance tests such as ionic conductivity, interfacial impedance, and cycle stability were carried out.

[0071] The battery was left to stand for 6 h before electrochemical testing. The ionic conductivity was measured by electrochemical impedance spectroscopy on a VSP-300 electrochemical workstation using a stainless steel (SS) electrode as the working electrode in the frequency range of 1 MHz to 1 Hz with an AC amplitude of 10 mV. Following the equation

[0072]

[0073] Calculate the ionic conductivity. L, R, and S are the thickness, AC impedance, and effective contact area of ​​the solid electrolyte, respectively.

[0074] The electrochemical performance of solid-state batteries was measured at room temperature using a Neware multi-channel battery test system at 0.1 mA cm -2 The cycling stability at different current densities and the performance of LRMO cells in the voltage range of 2.0 to 4.8 V were evaluated.

[0075] (1) The surface and cross-section of the C-PE electrolyte membrane (Example 1) were characterized using a scanning electron microscope (SEM): Figure 1 It shows that the surface morphology of the electrolyte membrane is relatively flat, and the thickness of the cross section shows the ultra-thin thickness of the polymer electrolyte, which is beneficial to improving the energy density of the battery when assembling the battery test.

[0076] (2) Calculation of ionic conductivities of different proportions of embodiments at room temperature using impedance at room temperature:

[0077] Figure 2 The ionic conductivity of the electrolyte membranes of Examples 1 to 3 is shown. The solid electrolyte membrane with 0.37 g of TFPMA (Example 1) exhibits the highest ionic conductivity, and further increasing or decreasing the TFPMA ratio decreases the conductivity. Comparison of Examples 1 to 3 ultimately determined the optimal mass ratio of VEC, TFPMA, and LiTFSI to be approximately 4:0.37:1.748. The electrolyte membrane prepared under these conditions exhibits the best conductivity, further enhancing battery performance.

[0078] (3) Utilization 1 The synthesized PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes were characterized by H NMR:

[0079] Figure 3 and Figures 4a to 4d The results show that the electrolyte membranes of PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) 1 H NMR, and the degree of polymerization was calculated. Among them, the C-PE electrolyte membrane (Example 1) used as the experimental sample had the highest degree of polymerization.

[0080] (IV) The synthesized different polymer electrolytes were characterized by FTIR:

[0081] Figure 5 The successful synthesis of PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes was demonstrated.

[0082] (V) Differential scanning calorimetry (DSC) was used to characterize the synthesized polymer electrolytes.

[0083] Figure 6 The glass transition temperatures (TG) of the prepared PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes are shown, among which the C-PE (Example 1) electrolyte membrane has the lowest TG (-86.7 degrees Celsius), showing that the C-PE (Example 1) electrolyte membrane has the softest polymer chain segment.

[0084] (6) The synthesized different polymer electrolytes were characterized by gel permeation chromatography (GPC):

[0085] Figure 7 The gel permeation chromatography of the prepared PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes and the weight average molecular weight (Mw) and number average molecular weight (Mn) of each polymer obtained by the test analysis are shown.

[0086] (VII) The synthesized different polymer electrolytes were characterized by thermogravimetric analysis (TG or TGA):

[0087] Figure 8 The weight loss of the prepared PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes as the temperature increases is shown to evaluate the residual proportion of their organic monomers.

[0088] (8) Calculate the ionic conductivity of different comparison ratios at room temperature using the impedance at room temperature:

[0089] Figure 9 The ionic conductivity of the prepared PVEC (Comparative Example 1), C-PVEC (Comparative Example 2), and P(VEC-TFPMA) (Comparative Example 3) electrolyte membranes is shown. Figure 2 Compared with the C-PE (Example 1) in the embodiment, it is confirmed that the embodiment after secondary polymerization has the best room temperature ionic conductivity.

[0090] (IX) Cycling stability of symmetrical batteries assembled with various polymer electrolytes was tested using a constant current charge-discharge method:

[0091] Figure 10 The results show that the lithium symmetric battery assembled with PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes can achieve a high charge / discharge rate at 0.1 mA cm -2 Long-term cycle performance under current density: It can be seen that the C-PE (Example 1) electrolyte membrane has the most stable cycle stability and the smallest overpotential.

[0092] (10) The cycling stability and rate performance of each polymer electrolyte when matched with the LRMO cathode were tested using the constant current charge-discharge method:

[0093] Figure 11 The long-term cycling test of PVEC (Comparative Example 1), P(VEC-TFPMA) (Comparative Example 3), and C-PE (Example 1) electrolyte membranes matched with LRMO cathodes is shown, as well as the rate performance of P(VEC-TFPMA) (Comparative Example 3) and C-PE (Example 1) electrolyte membranes matched with LRMO cathodes. It can be seen that the LRMO-based battery assembled with the C-PE (Example 1) electrolyte membrane has good cycle stability and capacity retention under high-voltage conditions, and has excellent rate performance.

[0094] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A polymer electrolyte membrane, comprising a nanofiber membrane substrate formed of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and a solid electrolyte membrane formed on the substrate, wherein the solid electrolyte membrane is formed by secondary polymerization of vinyl ethylene carbonate (VEC), 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA), and lithium bistrifluoromethanesulfonyl imide (LiTFSI), the degree of polymerization of the solid electrolyte membrane being 65 to 70%, the thickness of the nanofiber membrane substrate being 3 to 8 μm, and the ratio of the polymer mass of the solid electrolyte membrane to the area of ​​the nanofiber membrane substrate being 6 to 7 g:90 to 110 cm -2 .

2. The polymer electrolyte membrane according to claim 1, characterized in that The ionic conductivity of the solid electrolyte membrane at room temperature is greater than 0.5 mS / cm.

3. The method for preparing a polymer electrolyte membrane according to claim 1 or 2, comprising the following steps: S1. Preparation of electrospun skeleton nanofiber membrane: Dissolve polyvinylidene fluoride (PVDF) and polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) in a mixed solvent of N,N-dimethylformamide (DMF) and acetone to prepare an electrospinning solution with a total concentration of 5-10 wt%; Stir at 40-60°C for 24-72 hours, filter and degas, spin through an electrospinning apparatus to obtain a nanofiber membrane with a thickness of 3-8 μm, and dry at 70-90°C; S2. Preparation of the polymer bulk: vinyl ethylene carbonate (VEC), 2,2,3,3-tetrafluoropropyl methacrylate (TFPMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were mixed in a molar ratio of 1:(0.5-2):(0.1-0.5), and azobisisobutyronitrile (AIBN) was added as an initiator, the amount of azobisisobutyronitrile was 0.5-1.5% of the total weight of the monomers, after deoxygenation by Schlenk tube treatment, prepolymerized at 60-70 ° C for 4-8 hours, and then stannous octoate (Sn(Oct) 2 was added as a crosslinking catalyst, the amount of stannous octoate was 0.5-2% of the total weight of the prepolymer, and the temperature was raised to 75-85 ° C for coordination polymerization for 10-14 hours to obtain a fluorinated copolymer solution; S3. Membrane formation: The polymer solution obtained in step S2 is cast onto the nanofiber membrane of step S1, and heated and cured at 70-90°C under vacuum conditions for 12-24 hours to form a composite solid polymer electrolyte membrane. The ratio of the polymer mass of the solid electrolyte membrane to the base area of ​​the nanofiber membrane is 6-7g:90-110cm -2 .

4. The preparation method according to claim 3, characterized in that In step S1, the mass ratio of polyvinylidene fluoride (PVDF) to polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP) is (8-9.5):(0.5-2); Preferably, in step S1, the volume ratio of N,N-dimethylformamide to acetone is (6-8):(2-4); Preferably, in step S1, the spinning conditions are as follows: voltage 8-12 kV, distance between the needle and the receiving device 10-15 cm, and ambient humidity ≤10%.

5. The preparation method according to claim 3, characterized in that The deoxygenation treatment in step S2 is specifically as follows: after freezing with liquid nitrogen, evacuating to a pressure of ≤10 Pa, and introducing nitrogen to restore the pressure to normal, and repeating the operation at least 3 times.

6. The preparation method according to claim 3, characterized in that The thickness of the film formed during casting in step S3 can be adjusted by controlling the viscosity of the casting solution and the porosity of the electrospun skeleton nanofiber membrane. The thickness of the obtained electrolyte membrane is in the range of 5-50 μm.

7. Use of the polymer electrolyte membrane according to claim 1 or 2 as an electrolyte in a solid-state lithium battery.

8. A solid-state lithium battery, comprising the polymer electrolyte membrane according to claim 1 or 2 as an electrolyte.

9. The solid-state lithium battery according to claim 8, characterized in that The positive electrode sheet in the solid-state lithium battery is a lithium-rich manganese-based or high-nickel ternary positive electrode material, and the negative electrode sheet is one of a lithium sheet, a lithium alloy or hard carbon.

10. The solid-state lithium battery according to claim 9, characterized in that: The positive electrode sheet is made of one of lithium cobalt oxide, lithium iron phosphate, and nickel cobalt manganese.

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